The subject matter disclosed herein relates to a system and method for the recovery of crude oils within the earth and, in particular, to a system and method for recovering highly viscous oils.
The world depends heavily on hydrocarbon fuels, such as petroleum, as an energy source. Petroleum hydrocarbons, or “oil,” may be recovered from reservoirs within the earth using a variety of methods, such as drilling for example. Drilling works well for certain categories of oil where the oil viscosity allows the fluid to flow within the well casing to the surface. Where deep oil reserves are being exploited, pumps and other auxiliary equipment may be used to assist the extraction of oil.
One category of oil, sometimes referred to as “heavy oil” or “extra-heavy oil” or “bitumen” (hereinafter called “heavy oil”), is highly viscous oil that does not readily flow through the reservoir or production well casing, even with the assistance of pumps or other equipment. This flow or mobility issue may also be caused by compounds such as wax or paraffin. Heavy oil may be extracted using a variety of non-thermal techniques such as mining and cold heavy oil production with sand (CHOPS). However, most of these heavy oil reserves are positioned at depths greater than that from which it may be recovered using mining techniques, and other non-thermal methods such as CHOPS do not produce a high enough fraction of the original oil in place. In an effort to extract this oil, so-called “thermal methods” such as cyclic steam (“huff and puff”), steam flooding, and steam assisted gravity drainage (“SAGD”) have been developed. In these, steam is generated at the surface and transferred down into the well into contact with the oil reserve. The steam heats and reduces the viscosity of the oil enough to allow flow and displacement of the treated oil toward the production wellhead.
It should be appreciated that while such surface steam based generating processes do allow for the extraction of heavy oil from reservoirs that were previously unrecoverable by mining techniques, surface steam generation processes generally do incur high energy costs and there is a limit to the depth at which these techniques may be used. It should be appreciated that these processes involve energy losses at several stages: in the steam generation process; in distributing the steam at the surface; and, as the steam is transferred from the surface. Past a certain depth, the cost or technical feasibility of using surface generated steam is prohibitive. Even before that depth is reached, the energy and other costs of producing the oil can be very high. As a result, a large volume of the world's oil reserves are classified as “unrecoverable” due to the depth and viscosity of the oil, and even recoverable oil may face high production costs. It should further be appreciated that other geographic locations or geologic formations also may not be conducive to surface steam based methodologies. For example, in permafrost areas, surface heat based generation may not be acceptable as the heat may cause a thawing of the ground supporting the oil recovery equipment. Surface steam based generation systems may also be of limited use in oceanic reserves where the loss of thermal energy between the surface heat generator to the ocean floor may make the use of surface steam techniques economically and technically infeasible.
Accordingly, it should be appreciated that while existing heavy oil extraction techniques are suitable for their intended purposes a need for improvement remains, particularly in providing a system and method for extracting heavy oil reservoirs located deep within the earth.